The invention relates to a vacuum pump and a stator arrangement for a vacuum pump.
A vacuum pump may be formed by positive displacement pumps such as roots, claw or screw pumps. These pumps comprise a stator arrangement which defines a volume which is swept by a rotor arrangement for pumping gas from an inlet to an outlet of the stator arrangement. Heat is generated by the compression of the pumped gas and by inefficiencies in the mechanical and electrical components, when in use.
The generation of heat in vacuum pumps can decrease reliability and performance. For example, vacuum pumps may seize due to the deposition of metal based semiconductor precursors, which increases at higher temperatures and causes the reduction of clearances between the stator and rotor components. Corrosion, due to the reaction of gases such as fluorine with the surfaces of pump components, also causes a reduction in clearances at higher temperatures. It has also been noted that pump lubricant may be degraded or evaporated.
Typically, pumps are cooled by cooling plate assemblies or water jackets. In the former, aluminium cooling plates are secured to a surface of a pump stator. Tubes are pressed into the surface of the plates for conveying a liquid coolant, which is usually water. Heat is transferred to the water across three thermal interfaces. The first interface is that of the pump stator to the aluminium plates. The second interface is from the plates to the tubes, and the final interface is from the tubes to the water. Heat in the water is then carried away from the system. Although this method of cooling has been optimised over time it is still not a particularly efficient way of cooling. The amount of surface area over which the cooling plate assemblies can be applied limits the magnitude of heat that can be removed. It may also be possible to secure a cooling plate to only one of the surfaces of the stator or at least not all of the surfaces of the stator because of other components which may require attachment to the pump and block access for cooling.
In water jackets, the pump stator is hollow and water is conveyed through it removing the heat from the system. This method is thermally more efficient than the cooling plate assembly approach but practical drawbacks exist. The water jacket method of cooling is usually implemented in one of two ways; directly or indirectly. Direct cooling involves passing water directly through the core of the pump stator and thus corrosion becomes a concern since many pumps are constructed from iron. Indirect cooling means that the cooling water is provided by a closed system running with water conditioned with corrosion inhibitors. Such a system is complicated and expensive since a pump is required to circulate the water and a heat exchanger is required to cool the cooling water.
The discussion above is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter. The claimed subject matter is not limited to implementations that solve any or all disadvantages noted in the background.